Fertilizers are generally compounds that are applied to soils or directly to plants to supply one or more plant nutrients essential for the growth of plants. A variety of nutrients, or elements, are all equally important for healthy plant growth. However, there may be a significant difference in the amounts of specific nutrients required. For example, the elements nitrogen (N), phosphorus (P), and potassium (K) are generally referred to as primary nutrients due to the large amounts of each required for desirable plant or crop growth. Secondary nutrients are also important for plant growth but in certain circumstances are not required in amounts comparable to the primary nutrients. Secondary nutrients include calcium (Ca), magnesium (Mg), and sulfur (S). Other elements are required in minor amounts compared to the primary and secondary nutrients. Such elements, often referred to as micronutrients, may include boron (B), chloride (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn).
Solid fertilizers are often employed to distribute the essential nutrients to plants and crops. The fertilizers are generally processed into an aggregate of nutrients in granule, prill or powdered form. The granule materials, are ideally uniform in size. However, the fertilizers are prone to segregation and dusting problems especially when multiple nutrients are blended together in their various powder to granular forms. Segregation of the different nutrients leads to the uneven distribution of those nutrients upon application on fields and crops. The granules, powders or prills, are usually water-soluble for quick release to enable timely plant root uptake. The advanced large scale field applications of granules may not result in a combined nutrient offering that effectively addresses the plant growth requirements of all the inherent variation of soils.
Solid fertilizers may be inefficient at supplying plants or crops with sufficient nutrient demands depending on soil and other environmental conditions. There are several potential mechanisms that interfere with the nutrient delivery to the roots of a plant or crop for uptake. Upon dissolution and release of the nutrients from the granule form, the fertilizer may encounter nutrient delivery inefficiencies due to phenomena such as volatilization, denitrification, leaching, and immobilization through microbial and soil interactions. One of ordinary skill in the art understands the inefficiency dynamics of fertilizer loss. Nitrogen, in the form of urea, may volatilize at varying rates depending upon environmental conditions. Leaching of nutrients may contaminate groundwater sources or other pathways exiting the soil. Nutrient loss may also occur as run-off from rain water or irrigation. The run-off may create environmental concerns, such as eutrophication leading to hypoxia. Immobilization is the tie-up of available nutrients into forms unavailable for plants. For example, phosphate in its plant available form as an anion is strongly attracted to the cation calcium in the soil. These reactions begin to occur immediately once the P fertilizer is applied to the soil and thereafter becomes unavailable quickly to plants. Microbial activity can impact both positively and negatively the availability of soil nutrients.
Additionally, other minerals like zinc, iron, manganese and copper may not be readily available in the soil, not evenly distributed in the soil, or not accessible by the plant roots to affect the efficient uptake of the nutrients. Also, erratic rain or irrigation causing the wetting of the granule or the soil can negatively impact the uptake of the nutrients. For example, a rain event of as little as 12.7 mm over a top-dressed application of urea can exacerbate ammonia volatilization.
It is estimated that the delivery of macronutrients alone are only about sixty percent or less efficient and in some cases far less than thirty percent efficient at delivering crop nutrients in the first year after application. The loss of efficiency in fertilizing the soil and plants is due in large part to the above-noted factors. The inefficient use, or the resulting overuse of fertilizers due to such inefficiencies, has created economic, environmental and social concerns as the demand for greater crop efficiency continues to increase.